1. Field of the Invention
This invention relates to manometers for infusion apparatus and more particularly to a manometer for measuring the hydrodynamic pressure of fluids parenterally administered to a patient.
2. The Prior Art
Intravenous infusion of fluids into a patient has become a routine hospital procedure in many types of situations. Typically, the intravenous infusion apparatus consists of an indwelling catheter that is connected through tubing to a fluid source such as an elevated plastic bag.
Because of the resistance of the catheter, catheter tubing and back pressure from the patient, it is often-times necessary to supply a pressure source such as a pump-up pressure cuff. The pressure cuff is placed over the plastic bag containing the fluid and is inflated. In this manner the infusion fluid may be delivered at a particular pressure that is consistent with a desired flow rate for the infusion fluid.
In some types of situations it is of utmost importance to provide a carefully controlled flow rate of the infusion fluid. For example, proper administration of some types of medication may require carefully controlled flow rates over long periods of time. Since flow rate is dependent upon the hydrodynamic pressure of the infusion fluid, fluid pressures must be continuously monitored.
In the past, one of the problems associated with parenteral administration of fluids to a patient has been the problem of accurately measuring the hydrodynamic pressure of the fluid being infused into the patient. Typically it has been assumed that the pressure exerted by the pressure cuff on the fluid source bag is the same as the pressure exerted on the fluid at its point of infusion into the patient. The level of pressure at the pressure cuff is read directly from a gage that is associated with the pressure cuff.
However, in practice, the hydrodynamic pressure of the fluid being infused into the patient is not the same as the hydrostatic pressure measured at the pressure cuff. The resistance of the tubing and catheter system and the back pressure of the patient all have an effect on the hydrodynamic pressure of the fluid that is infused into the patient.
To eliminate these inaccuracies manometers have been developed that may be directly placed in the tubing line and that may be operated to temporarily interrupt the fluid flow so that hydrostatic pressure measurements may be periodically taken. See, for example, U.S. Pat. No. 3,807,389.
Although these types of in-line manometers provide more accurate pressure readings of the infusion fluid, they do not permit continuous monitoring of hydrodynamic pressures. Since they measure hydrostatic pressure, such manometers require periodic interruption of the fluid flow to obtain a pressure reading. This of course may be inconvenient in some types of situations and may even be hazardous if the required pressure level drops or rises significantly between readings, resulting in over or under infusion.
From the foregoing, it will be appreciated that what is needed in the art is an in-line manometer which may be used to continuously monitor the hydrodynamic pressure of fluids that are parenterally administered to a patient. Such an invention is illustrated and described herein.